什么时候需要切换rootViewController

Question

我一直在做一个 Swift 项目，我有两个视图控制器，登录视图控制器和主视图控制器。当用户启动应用程序时，如果用户未登录，我想显示登录视图控制器，另一方面，如果用户已登录，我想显示主视图控制器。

所以流程会是这样的。

当用户未登录时，显示

1. 登录视图控制器
2. 主页视图控制器

   当用户已经登录时，显示

   1. 主页视图控制器

      在场景委托中，我写了

      func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
          guard let scene = (scene as? UIWindowScene) else { return }
      
          window = UIWindow(frame: scene.coordinateSpace.bounds)
          window?.windowScene = scene
          window?.rootViewController = HomeViewController() or LoginViewController() depending on the user's login status
          window?.makeKeyAndVisible()
      }
      

      我想知道是否应该将 HomeViewController 应用为 rootviewcontroller 而不管用户的登录状态如何（并且可能在用户未登录时在 homeVC 上显示 loginVC），或者我应该根据用户的登录状态切换视图控制器。

      那么，这种情况下，切换rootviewcontroller有什么意义呢？为什么切换根视图控制器是（或不重要）？

      当我将视图控制器应用于根视图控制器属性时，我应该考虑什么？

Answer 1

// SceneDelegate.swift
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    // Use this method to optionally configure and attach the UIWindow `window` to the provided UIWindowScene `scene`.
    // If using a storyboard, the `window` property will automatically be initialized and attached to the scene.
    // This delegate does not imply the connecting scene or session are new (see `application:configurationForConnectingSceneSession` instead).
    guard let _ = (scene as? UIWindowScene) else { return }

    // if user is logged in before
    if let loggedUsername = UserDefaults.standard.string(forKey: "username") {
        window?.rootViewController = HomeViewController()
    } else {
        // if user isn't logged in
        window?.rootViewController = LoginViewController()
    }
}

Answer 2

我认为可能还有其他情况，例如 Root 是一个容器 View Controller 由 HomeVC 和 LoginVC 组成。 例子）

final class RootVC: UIViewController {
 private let loginVC = LoginVC()
 private let homeVC = HomeVC()
 
 override func viewDidLoad() {
  super.viewDidLoad()
   addChild(homeVC)
   view.addSubview(homeVC.view)
   addChild(loginVC)
   view.addSubview(loginVC.view)
 }

 func showVC() {
  if isLogin {
   homeVC.hide()
   loginVC.show()
  } else {
   reverse()
  }
 }
}

Answer 3

大家好，我有一个想法可以在SceneDelegate 中设置一个 RootViewController。首先，我们需要在SceneDelegate 类中创建方法setViewController 和变量currentScene，请随时参考下面的代码。 根据您的示例 HomeViewController、LoginViewController 有两个不同的视图控制器

import UIKit

class SceneDelegate: UIResponder, UIWindowSceneDelegate {
  
  var window: UIWindow?
  var currentScene: UIScene?
  
  func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    guard let _ = (scene as? UIWindowScene) else { return }
    currentScene = scene
    if UserDefaults.standard.bool(forKey: "isLoggedIn") == true{
      self.setRootViewController(LoginViewController())
    }else{
      self.setRootViewController(HomeViewController())
    }
  }
  
  func setRootViewController(_ viewController: UIViewController){
    
    guard let scene = (currentScene as? UIWindowScene) else { return }
    
    window = UIWindow(frame: scene.coordinateSpace.bounds)
    window?.windowScene = scene
    window?.rootViewController = viewController
    window?.makeKeyAndVisible()
    
  }
  
}

class ButtonViewController: UIViewController {
  
  lazy var button: UIButton! = {
    
    let button = UIButton()
    button.translatesAutoresizingMaskIntoConstraints = false
    button.backgroundColor = .darkGray
    button.setTitleColor(.white, for: .normal)
    button.addTarget(self, action: #selector(buttonAction), for: .touchUpInside)
    button.tag = 1
    button.setTitle("Tap", for: .normal)
    return button
    
  }()
  
  
  override func loadView() {
    super.loadView()
    self.view.backgroundColor = .white
    
    setConstraint()
  }
  
  override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    
  }
  
  func setConstraint(){
    
    self.view.addSubview(self.button)
    
    NSLayoutConstraint.activate([
      
      self.button.heightAnchor.constraint(equalToConstant: 60),
      self.button.widthAnchor.constraint(equalToConstant: UIScreen.main.bounds.width * 0.66),
      self.button.centerXAnchor.constraint(equalTo: self.view.centerXAnchor),
      self.button.centerYAnchor.constraint(equalTo: self.view.centerYAnchor),
      
    ])
    
  }
  
  @objc func buttonAction(){  }
  
}

class HomeViewController: ButtonViewController{
  
  override func loadView() {
    super.loadView()
    self.view.backgroundColor = .red
    self.button.setTitle(String(describing: HomeViewController.self), for: .normal)
  }
  
  override func buttonAction() {
    let sceneDelegate = UIApplication.shared.connectedScenes.first?.delegate as! SceneDelegate
    sceneDelegate.setRootViewController(LoginViewController())
  }
  
}


class LoginViewController: ButtonViewController{
  
  override func loadView() {
    super.loadView()
    self.view.backgroundColor = .green
    self.button.setTitle(String(describing: LoginViewController.self), for: .normal)
  }
  
  override func buttonAction() {
    let sceneDelegate = UIApplication.shared.connectedScenes.first?.delegate as! SceneDelegate
    sceneDelegate.setRootViewController(HomeViewController())
  }
  
}

如果单击按钮视图控制器可以更改为 rootViewController。 输出：